Deoxyribonucleic acid, the molecular storehouse of genetic codes better known as DNA, has become a priceless tool for law enforcement agents in recent years. Thanks to advances that allow scientists to extract DNA from a single hair follicle, or even just a handful of skin cells, police and prosecutors have been able to identify and convict hundreds of criminals. But it's not enough to gather DNA evidence from a crime scene. Police also have to match that evidence to the DNA of a known person, and that has raised a host of privacy issues.

One case in the state of Washington is challenging how police go about getting DNA from their suspects.

Just as with fingerprints, no two people have the same DNA, not even identical twins. That's why recent advances in DNA identification have been such a boon to the forensics industry. But DNA evidence is basically useless without a match to a particular person. And according to John Junker, who teaches criminal law at the University of Washington, making that match can pose a challenge to police, since DNA is considered to be the personal property of each individual.

"Obviously they cannot go out and simply do random screens," he said. "They have to be able to either have probable cause to believe that a sample of the person's blood or other tissues would provide evidence of a crime, or they have to get the evidence with the consent of the individual, or they could do it in an undercover way."

It's that last way of getting a match, the undercover way, that's raising some legal questions. The courts have ruled police don't need a court order to go through a suspect's trash, looking for fingernail clippings or hair, once that trash has been placed on the sidewalk for pick-up. Police are also allowed to follow a suspect, waiting for him to discard a cigarette butt or coffee cup, both of which would have saliva on them could, therefore, yield valuable DNA evidence. But that's not what happened this past July, when police in Washington arrested John Athan for the 1982 rape and murder of a 13-year-old girl.

Police arrested Mr. Athan when they matched DNA from his saliva to semen found on the victim's body. But is his attorney, John Muenster said "they did not get court authorization or a warrant to do what they did."

John Athan had been a suspect at the time of the murder. But in 1982, DNA identification techniques weren't advanced enough to be of any help to police. Twenty-one years later, law enforcement agents in Seattle sent John Athan a letter, telling him he could be eligible to participate in a class-action lawsuit on behalf of people who'd been overcharged on parking tickets. All Mr. Athan had to do was sign a form and mail it back to the senders. The letter was a complete lie, but John Athan didn't know that. He signed the form, licked the envelope, and unwittingly sent his DNA to police, who now had the technology to use it.

"I've filed a motion to suppress the DNA-related evidence," said attorney Muenster, "and I've also filed a motion to dismiss the case under a Washington state court rule that authorizes judges to dismiss cases based on arbitrary action or government misconduct."

But does the dishonest manner in which police convinced John Athan to give up his DNA constitute government misconduct? The University of Washington's John Junker doesn't think so.

"There are mountains of precedent for doing it," he said. "I mean all undercover work by undercover police officers is fruitful only if they can persuade the persons whom they are investigating that they are not police officers, and to get the suspect to unwittingly disclose to them some information that would be an admission of their involvement in crime."

But the police in this case did more than just convince John Athan they weren't police. They convinced him they were lawyers, representing people who'd gotten parking tickets. And that's how they broke the law, according to Mr. Athan's attorney, John Muenster. Mr. Muenster says in the state of Washington, it's illegal for anyone who isn't a licensed lawyer to pretend to be one.

"Americans have rights to consult with counsel, and lawyers on the other side have the duty to maintain client confidence," he said. "If the police are allowed to pose as lawyers, those pillars of our system are going to crumble. So I see this as a watershed."

Prosecutors in Seattle aren't commenting on the case, since the trial date is less than a month away. John Muenster's motion to have the evidence, and the charges, thrown out will be heard by a judge this week. If that judge decides not to throw out the case, John Athan's trial for the rape and murder of a teenager 21 years ago will begin on November 13.